The present invention relates to spool for a seat belt retractor.
A seat belt safety restraint generally comprises belt webbing wound on a spool that is mounted for rotation about its longitudinal axis to wind in or pay out webbing. The spool is biased in a winding-in direction by a spiral spring. A sensor detects a crash, for example by detecting acceleration or deceleration over a predetermined level. The sensor then activates a locking mechanism to lock the spool against rotation and prevent further pay out of webbing thus restraining the occupant against forward motion.
During manufacturing of a retractor the belt webbing is usually threaded onto the spool through a slot in its core. A strong steel webbing pin is sewn into the end of the webbing to prevent the end pulling through the slot.
However it has been found that under extreme conditions, the pin can cause the spool to weaken and break along the line of the slot. This is a particular problem in more modern spools, which are often made of aluminum to take advantage of its lightness.
One way to spread the load exerted by the webbing is to use two slots in the spool. The webbing is passed in one direction through a first slot, and then back, in the opposite direction through the other generally parallel slot. In this way the webbing imposed forces are spread over a greater area of the spool and the spool can withstand higher tensile loads.
However, this form of construction for the spool is more difficult to assemble and production time is increased, with attendant increased costs. The double threading motion is difficult to automate and generally this step in assembly is found to be the slowest part of a spool assembly production line.
The present invention provides an improved retractor spool arrangement with faster assembly times.